Finding out about horse's past...

Didn't know where else to put this...
How could I go about finding out about my horse's past and his previous owners? I know their names but I can't find anything about them...I did find his old for sale ad...all I know is that he had two owners in Florida, had some training in Alabama, then went to the home in Tennessee where I bought him from. How could I find out more about his past and his owners?

Well, I've found one owner on Facebook and we're talking so that's a start!